In a saucepan heat up the oil, add the onion and sugar and fry over a low heat for about 6 minutes stirring often. Add the remaining ingredients and simmer for a further 10 minutes stirring often to ensure the mixture does not stick to the pan.
Remove from the heat and puree the sauce until smooth. Set aside to cool completely then transfer into a jar or bowl. Cover and refrigerate for up to a week.
In different regions of the world Marmite is called Vegemite and AussieMite so you should be able to get it wherever you are.
Worcestershire sauce usually contains anchovy extract but you can get a vegetarian alternative so read the label carefully.
Adjust the proportions to your liking. For example use a little more vinegar for a tangier sauce.
This bbq sauce is mild but you can spice it up by adding cayenne pepper or chilli powder.
You may not need to use any salt as both the marmite and Worcestershire sauce are very salty.
Refrigerate in a jar or bowl, covered, for up to a week.